1. Field of the Invention
Embodiments of the present invention generally relate to a method, computer-readable medium, and system for determining properties of a magnetic read head.
2. Description of the Related Art
Modern computer systems typically include a hard drive which may be used as mass storage for the computer system. Information in the hard drive is typically stored as magnetic charge on one or more magnetic disks within the hard drive. To read the information, the hard drive includes a magnetic read head which senses the magnetic charge as the magnetic disks spin beneath the read head.
Modern magnetic read heads typically include several layers of material deposited on a substrate. As the magnetic read head passes over an area of a magnetic disk in which a magnetic charge is present, the magnetic charge may induce a detectable change in the layers of material in the magnetic read head. For example, during a read operation, a current may be applied to the layers of material in the magnetic read head. In some cases, the current may be applied perpendicular to the layers of material in the magnetic read head. Where the current is applied perpendicular to the layers of material in the magnetic read head (e.g., perpendicular to the plane of the layers of material), the read head may be referred to as a current-perpendicular to plane (CPP) magnetic read head.
The current applied to the layers of material may create a voltage across the layers of material which is proportional the resistance of the layers of material. As the head passes over a magnetic charge on the magnetic disk, the magnetic charge may cause a change in the combined resistance of the layers of material (e.g., an increase or decrease in the resistance of the layers of material). The stored magnetic charge may then be measured via a corresponding change in the voltage across the layers of material (e.g., a corresponding increase or decrease in the voltage resulting from the current applied to the layers of material).
In order to ensure proper design of the hard drive for reading magnetic charges stored on the magnetic disk, there may be a desire to measure certain properties of the magnetic read head. For example, the magnetic read head may have an active strip height and an active track width which indicate the area of the magnetic read head which is affected by magnetic charge stored on the magnetic disk. Other measurable properties of the magnetic read head may include intrinsic properties of the magnetic read head such as the minimum resistance of the layers of the magnetic read head and the percent change in resistance of the layers of the magnetic read head between the minimum and maximum resistance due, e.g., to the alignment of the magnetic moments of the free layer and the pinned layer as described below.
While the magnetic read head may be designed and manufactured according to specified values of given properties of the magnetic read head (referred to as nominal values, e.g., nominal active stripe height and nominal active track width), the resulting manufactured magnetic read head typically deviates from such nominal design values, for example, due to imperfections in the manufacturing process. As an example, during manufacturing of a CPP magnetic read head, the sides of the magnetic read head may be milled to obtain a magnetic read head with a track width and stripe height close to a specified nominal value. During milling of the sides of the magnetic read head, the material being milled (e.g., material from the layers of the magnetic read head) may be redeposited along the sides of the magnetic read head. Such redeposited material is referred to herein as shunting material because the shunting material creates a shunt (e.g., an alternate current path) along the sides of the CPP magnetic read head.
In some cases, the shunting material may be magnetically dead, such that the material is insensitive to changes in magnetization of the magnetic read head, (e.g., due to the presence of a stored magnetic charge), thereby decreasing the sensitivity of the magnetic read head. Also, the milling process may cause damage to the layers of the magnetic read head, further changing the properties of the magnetic read head from the nominal design values and decreasing the sensitivity of the magnetic read head. The presence of such imperfections in the manufacturing process may make measurement of properties of the magnetic read head (e.g., active track width, active track height, minimum resistance, and percent change in resistance) difficult, thereby complicating proper design of the hard drive.
Accordingly, what is needed is an improved method, computer readable medium, and system for determining properties of a magnetic read head.